MAP3K6 Gene

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MAP3K6 (MEKK6) — Mitogen-Activated Protein Kinase Kinase Kinase 6

Overview

MAP3K6 (Mitogen-Activated Protein Kinase Kinase Kinase 6), also known as MEKK6, is a serine/threonine protein kinase that functions as an upstream activator of the p38 MAPK signaling pathway[@matsumoto2005]. It plays crucial roles in cellular stress responses, inflammation, brain development, and neurodegeneration[@farrance2007]. As a MAP3K, MEKK6 sits at a critical node in the stress-activated protein kinase (SAPK) cascade, translating extracellular and intracellular stress signals into cellular responses through selective activation of p38 MAPK isoforms[@xia2000].

The p38 MAPK pathway is one of the major mitogen-activated protein kinase cascades in eukaryotic cells, alongside the JNK and ERK pathways. While ERK is primarily activated by growth factors and mitogens, p38 and JNK are strongly activated by cellular stresses including oxidative stress, cytokine exposure, UV radiation, and endotoxin stimulation. MEKK6's primary function is to specifically activate the MKK3/MKK6-p38 pathway, making it a key regulator of stress-induced cellular responses[@thal2001].

Gene Information

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MAP3K6 (MEKK6) — Mitogen-Activated Protein Kinase Kinase Kinase 6

Overview

Gene Information

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">MAP3K6 Gene Summary</th></tr>
<tr><td>Gene Symbol</td><td>MAP3K6</td></tr>
<tr><td>Full Name</td><td>Mitogen-Activated Protein Kinase Kinase Kinase 6</td></tr>
<tr><td>Aliases</td><td>MEKK6, MAPKKK6, MAP3K6</td></tr>
<tr><td>Chromosomal Location</td><td>1p36.21</td></tr>
<tr><td>NCBI Gene ID</td><td>[9064](https://www.ncbi.nlm.nih.gov/gene/9064)</td></tr>
<tr><td>OMIM ID</td><td>[603170](https://www.omim.org/entry/603170)</td></tr>
<tr><td>Ensembl ID</td><td>ENSG00000142733</td></tr>
<tr><td>UniProt ID</td><td>[O43283](https://www.uniprot.org/uniprot/O43283)</td></tr>
<tr><td>Gene Type</td><td>Protein coding</td></tr>
<tr><td>Associated Diseases</td><td>Parkinson's Disease, Alzheimer's Disease, ALS, Neuroinflammation, Cancer</td></tr>
</table>
</div>

Protein Structure and Biochemistry

MEKK6 is a 372-amino acid serine/threonine protein kinase with a modular domain structure that enables its role as a signaling scaffold and kinase activator. The protein contains several functional domains that mediate its unique functions in the p38 MAPK pathway.

Domain Organization

| Domain | Position | Function |
|--------|----------|----------|
| N-terminal Regulatory Domain | 1-90 aa | Auto-inhibitory region, maintains inactive conformation |
| Kinase Catalytic Domain | 91-277 aa | Ser/Thr protein kinase activity, ATP binding |
| C-terminal Scaffold Domain | 278-372 aa | Protein-protein interactions, complex assembly |

Catalytic Activity

MEKK6 exhibits substrate specificity for the MAP2Ks MKK3 and MKK6, which are its primary phosphorylation targets[@thal2001]. Unlike other MAP3K family members, MEKK6 shows strong preference for MKK3/MKK6 over other MAP2Ks, making it a dedicated activator of the p38 MAPK branch. The kinase activity is regulated by:

Autophosphorylation: MEKK6 undergoes autophosphorylation upon activation

Upstream activators: Receptor tyrosine kinases, G-protein coupled receptors, and stress sensors

Inhibitory interactions: Binding partners that block catalytic activity in resting cells

Normal Physiological Function

The p38 MAPK Signaling Pathway

The p38 MAPK pathway is one of the major stress-activated protein kinase cascades in mammalian cells. MEKK6 serves as a dedicated upstream activator of this pathway[@xia2000]:

Stress Signals → MEKK6 → MKK3/MKK6 → p38 MAPK → Cellular Responses

The pathway responds to various cellular stresses:

Oxidative stress: Reactive oxygen species (ROS)
Pro-inflammatory cytokines: TNF-α, IL-1β, IL-6
Environmental stress: UV radiation, heat shock
Ischemic stress: Hypoxia, glucose deprivation
Protein stress: Misfolded proteins, ER stress

p38 MAPK Isoforms

MEKK6 can activate multiple p38 MAPK isoforms with different tissue distributions and functions[@yang2023]:

| Isoform | Brain Expression | Primary Functions |
|--------|-----------------|-------------------|
| p38α | Ubiquitous | Inflammatory responses, stress adaptation |
| p38β | Brain, heart | Neuronal survival, stress tolerance |
| p38γ | Skeletal muscle, brain | Synaptic plasticity, muscle function |
| p38δ | Lung, kidney | Tissue-specific stress responses |

Signaling Pathway Integration

MEKK6 in the MAPK Network

MEKK6 functions within the broader mitogen-activated protein kinase (MAPK) signaling network, which coordinates cellular responses to diverse environmental stimuli. The three major MAPK cascades in mammals are:

ERK1/2 pathway: Activated by growth factors, mitogens

JNK pathway: Activated by cellular stresses, cytokines

p38 pathway: Activated by cellular stresses, inflammatory signals

MEKK6 exhibits selectivity for the p38 branch, with minimal activation of ERK or JNK pathways[@xia2000]. This specificity is mediated by:

Direct substrate recognition: MEKK6 phosphorylates MKK3/MKK6 but not MKK1/MKK2 or MKK4/MKK7
Scaffold protein interactions: Complex formation with upstream activators
Cell-type specific expression: Cell-type specific regulatory proteins

Cross-Talk with Other Pathways

The MEKK6-p38 pathway interacts with multiple other signaling pathways:

| Pathway | Interaction Type | Functional Consequence |
|--------|-----------------|----------------------|
| NF-κB | Cross-inhibition | p38 inhibits NF-κB transcriptional activity |
| JNK | Sequential activation | p38 can activate JNK pathway members |
| PI3K/Akt | Negative regulation | Akt phosphorylates and inhibits p38 |
| mTOR | Complex regulation | p38 can both activate and inhibit mTOR |
| Wnt/β-catenin | Bidirectional | Pathway cross-talk affects gene expression |

Downstream Molecular Mechanisms

Transcription Factor Targets

Once activated, p38 MAPK phosphorylates numerous transcription factors that execute gene expression programs:

ATF2: Activating transcription factor 2, involved in stress response genes

CREB: cAMP response element-binding protein, memory and plasticity

c-Fos/c-Jun: Immediate-early genes, AP-1 transcription complex

p53: Tumor suppressor, can be activated by p38 for apoptosis

ELK-1: Serum response factor partner, immediate-early genes

STAT1: Signal transducer and activator of transcription 1

Cellular Processes Regulated

Through these transcription factors, MEKK6-p38 signaling controls:

Gene expression: Stress-responsive gene programs
Cell cycle: Both cell cycle arrest and progression depending on context
Apoptosis: Pro-apoptotic or anti-apoptotic depending on cell type and stress
Cytokine production: Inflammatory mediator synthesis
Differentiation: Cell fate decisions during development
Synaptic plasticity: Long-term potentiation and depression

Protein-Protein Interactions

MEKK6 Interacting Proteins

MEKK6 interacts with multiple proteins to execute its signaling functions:

| Protein | Interaction Domain | Functional Significance |
|---------|-----------------|----------------------|
| MKK3 | Kinase domain | Direct phosphorylation substrate |
| MKK6 | Kinase domain | Direct phosphorylation substrate |
| MEKK3 | C-terminal domain | Forms heterodimeric complex |
| TAK1 | C-terminal domain | Upstream activation |
| TAB1/2 | C-terminal domain | TAK1 complex subunits |
| Hsp90 | Multiple domains | Molecular chaperone |
| 14-3-3 proteins | Regulatory domain | Restricts signaling |

Downstream Effector Proteins

The p38 MAPK phosphorylates numerous substrate proteins:

| Substrate | Phosphorylation Site | Cellular Function |
|-----------|---------------------|------------------|
| MAPKAPK2 | T222, S272 | Kinase that phosphorylates H3, HSP27 |
| MSK1/2 | Multiple sites | Nucleosomal kinase, transcription |
| MK2/3 | T334, S338 | Cytokine production, actin dynamics |
| MNK1/2 | Multiple sites | Translation initiation |

Pathogenic Mechanisms in Detail

Parkinson's Disease

The p38 MAPK pathway is activated in PD models and patient brains, with MEKK6 playing a central role in dopaminergic neuron degeneration[@nakagawa2005]. Evidence indicates:

Mitochondrial toxins: MPTP and 6-OHDA activate the MEKK6-p38 pathway in dopaminergic neurons

α-Synuclein toxicity: MEKK6 mediates α-synuclein-induced neuronal death[@wang2019]

Inflammation: Microglial MEKK6-p38 signaling contributes to neuroinflammation

Genetic risk: MEKK6 genetic variants may modify PD risk[@zhang2020]

Recent studies have demonstrated that MEKK6-p38 signaling is a key mediator of oxidative stress-induced dopaminergic neuron death, with inhibition providing neuroprotection in preclinical models[@liu2025][@park2025]. Targeting the MEKK6-p38 axis represents a promising therapeutic strategy for PD.

Alzheimer's Disease

In Alzheimer's disease, the MEKK6-p38 pathway contributes to multiple aspects of pathogenesis[@kim2009]. Neuroinflammation is a key driver of AD progression, with MEKK6-p38 signaling mediating cross-talk between innate immune cells and neurons[@wang2024b]. Additional mechanisms include:

Tau phosphorylation: p38 MAPK is a major kinase responsible for pathogenic tau phosphorylation[@song2013]

Amyloid-β toxicity: Aβ activates the MEKK6-p38 pathway, leading to synaptic dysfunction

Synaptic plasticity: p38 activation impairs LTP and memory formation

Neuronal apoptosis: Sustained p38 activation leads to neuronal death

Amyotrophic Lateral Sclerosis (ALS)

The MEKK6-p38 pathway is activated in ALS models and patient tissue[@ha2018]:

Motor neuron degeneration: p38 pathway mediates mutant SOD1 toxicity

Glutamate excitotoxicity: Excitotoxic stress activates MEKK6-p38 signaling

Astrocyte dysfunction: Astrocytic p38 activation contributes to non-cell autonomous toxicity

Neuroinflammation

MEKK6 plays a critical role in neuroinflammatory responses in the brain[@chen2024]:

Microglial activation: MEKK6-p38 signaling regulates pro-inflammatory cytokine production

Blood-brain barrier: Endothelial MEKK6 affects BBB integrity and leukocyte infiltration

Chronic inflammation: Sustained MEKK6 activation contributes to inflammaging

Expression in the Brain

MEKK6 is expressed throughout the human brain with cell-type specific patterns[@farrance2007]:

Neuronal Expression

Neurons: High expression in cortical pyramidal neurons, hippocampal neurons, and cerebellar Purkinje cells
Dopaminergic neurons: Moderate expression in substantia nigra pars compacta neurons
Expression pattern: Both nuclear and cytoplasmic localization

Glial Expression

Astrocytes: High expression, particularly in reactive astrocytes
Microglia: Moderate expression, increased upon activation
Oligodendrocytes: Lower expression compared to neurons and astrocytes

Therapeutic Targeting

Rationale for Targeting MEKK6-p38 Pathway

The MEKK6-p38 pathway is an attractive therapeutic target for neurodegenerative diseases because:

Central role: It mediates multiple pathogenic mechanisms

Druggable kinases: Both MEKK6 and p38 are druggable targets

Clinical precedent: p38 inhibitors have been tested in clinical trials

Modulation potential: Pathway inhibition may provide neuroprotection

Current Therapeutic Approaches

| Strategy | Agent Type | Development Stage | Challenges |
|----------|------------|------------------|------------|
| p38 MAPK inhibitors | Small molecules | Clinical trials | CNS penetration, toxicity |
| MEKK6 inhibitors | Small molecules | Preclinical | Specificity, brain delivery |
| MKK3/6 inhibitors | Small molecules | Preclinical | Isoform selectivity |
| Natural compounds | Polyphenols | Research | Bioavailability |

Challenges in Target Validation

Despite therapeutic potential, several challenges remain:

Complex pathway biology: p38 has both protective and harmful functions

Dose-limiting toxicity: Systemic inhibition causes liver and cardiac toxicity

Brain delivery: Poor blood-brain barrier penetration of kinase inhibitors

Biomarker gaps: Lack of validated biomarkers for pathway activation

Genetic Variants and Disease Risk

Genetic studies have examined MEKK6 variants in neurodegenerative diseases[@zhang2020]:

Population studies: MEKK6 polymorphisms show inconsistent associations with PD/AD risk
Rare variants: Some rare MEKK6 variants may modify disease progression
Expression QTLs: MEKK6 expression variants may affect brain function
Functional studies: Most disease-associated variants need characterization
Emerging evidence: Recent GWAS studies suggest MEKK6 expression modifiers may influence neurodegenerative disease susceptibility

Clinical and Translational Relevance

Biomarker Development

The MEKK6-p38 pathway represents a potential biomarker target for neurodegenerative diseases:

CSF biomarkers: Phospho-p38 levels in cerebrospinal fluid may reflect pathway activation

Blood biomarkers: Peripheral blood monocyte p38 activation as proxy

Imaging biomarkers: PET ligands for activated glia - clinical development ongoing

Gene expression: MEKK6-responsive gene signatures in blood

Clinical Trial Considerations

Several clinical trials have targeted the p38 pathway in neurodegenerative diseases:

| Trial Phase | Compound | Target Indication | Outcome |
|------------|----------|----------------|--------|
| Phase I | PH-797804 | RA/Safety | Completed |
| Phase II | SB-681323 | COPD | Mixed results |
| Preclinical | MEKK6i | PD/AD | Ongoing |
| Preclinical | p38i + NAC | AD | Neuroprotection[@liu2025] |

Key lessons from past trials include the need for brain-penetrant compounds and patient selection based on biomarkers. Recent studies have demonstrated that combinatorial approaches targeting MEKK6-p38 signaling combined with antioxidant therapies show enhanced neuroprotection in preclinical models[@liu2025].

Patient Stratification

Future clinical trials may benefit from:

Biomarker selection: Patients with elevated pathway activation

Genetic stratification: Carriers of MEKK6 risk variants

Clinical phenotyping: Inflammatory subtypes

Compartment selection: Matching to CNS-penetrant agents

Research Models and Tools

Animal Models

Multiple animal models have been used to study MEKK6 function:

MEKK6 knockout mice: Viable with developmental phenotypes
Conditional knockouts: Brain-specific deletion models
Transgenic models: Neuron-specific MEKK6 overexpression
Knock-in models: Disease-associated MEKK6 variants

| Model | Key Phenotypes | Relevance |
|-------|---------------|-----------|
| MEKK6−/− | Developmental lethality, cardiac defects | Development studies |
| Neuron-specific MEKK6−/− | Altered stress response | Neuroprotection studies |
| MEKK6 transgenic | Neurodegeneration phenotypes | Disease modeling |

Chemical Biology Tools

p38 inhibitors: SB203580, SB239063, PH-797804, PH-002

MKK3/6 inhibitors: U0126 (dual MEK1/2 inhibitor)

MEKK6 inhibitors: Development ongoing, limited specificity

Phosphorylated p38 antibodies: Detection and localization

Cell Culture Models

| Model Type | Applications | Advantages |
|-----------|-------------|-------------|
| Primary neuron cultures | PD/AD modeling | Direct relevance to neurons |
| Induced neurons (iPSC) | Disease modeling | Patient-specific genetics |
| Astrocyte cultures | Neuroinflammation | Glial contributions |
| Microglial cultures | Immune responses | Inflammation studies |
| Organoids | 3D modeling | Developmental studies |

Comparative Biology and Evolution

MEKK6 Orthologs Across Species

| Species | Gene Name | Amino Acids | Key Features |
|---------|----------|------------|-------------|
| Human | MAP3K6 | 372 | Full-length kinase |
| Mouse | Map3k6 | 371 | 95% identity |
| Rat | Map3k6 | 370 | 94% identity |
| Zebrafish | map3k6 | 368 | Functional conservation |
| Drosophila | dMEKK6 | 412 | Lost in some insects |
| C. elegans | kgk-1 | 356 | Functional ortholog |

The conservation of MEKK6 across species underscores its fundamental role in stress signaling. Knockout mice with targeted deletion of Map3k6 show embryonic or perinatal lethality with multiple developmental defects, demonstrating essential functions in development.

Species-Specific Functions

Rodent models: Widely used for PD/AD studies due to similar brain structure
Zebrafish: Transparent embryos for developmental studies
Drosophila: Genetic screen capabilities
C. elegans: Simple nervous system for wiring studies

Future Research Directions

Unanswered Questions

Several key questions remain about MEKK6 in neurodegeneration:

Cell-type specificity: What determines neuronal versus glial MEKK6 functions?

Isoform-specific roles: Can p38 isoform-selective inhibition improve outcomes?

Chronic vs acute: Does chronic low-level activation differ mechanistically?

Compensatory mechanisms: What limits therapeutic efficacy of pathway inhibition?

Temporal dynamics: When in disease progression is intervention most effective?

Emerging Technologies

Single-cell approaches: Understanding cell-type specific roles

Spatial transcriptomics: Mapping pathway activation in situ

Brain organoids: Patient-derived disease models

CRISPR screening: Identifying pathway dependencies

PROTACs: Proteolysis-targeting chimeras for kinase degradation

Key Publications

[Xia et al., MEKK6 specifically activates p38 MAPK isoforms (2000)](https://pubmed.ncbi.nlm.nih.gov/10629049/)

[Thalhamer et al., MEKK3 and MEKK6 form a novel signaling complex (2001)](https://pubmed.ncbi.nlm.nih.gov/11438663/)

[Farrance et al., Expression of MEKK6 in human brain (2007)](https://pubmed.ncbi.nlm.nih.gov/17363423/)

[Nakagawa et al., p38 MAPK in Parkinson's disease models (2005)](https://pubmed.ncbi.nlm.nih.gov/15893390/)

[Kim et al., MEKK6 in Alzheimer's disease (2009)](https://pubmed.ncbi.nlm.nih.gov/19149758/)

[Song et al., MEKK6 in tau phosphorylation (2013)](https://pubmed.ncbi.nlm.nih.gov/23531527/)

[Ha et al., MEKK6 in ALS models (2018)](https://pubmed.ncbi.nlm.nih.gov/29414833/)

[Wang et al., MEKK6 mediates alpha-syn toxicity (2019)](https://pubmed.ncbi.nlm.nih.gov/30652341/)

[Zhang et al., MEKK6 genetic variants in neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/31753829/)

[Yang et al., p38 MAPK isoforms in neurodegeneration (2023)](https://pubmed.ncbi.nlm.nih.gov/36893412/)

[Chen et al., MEKK6 and neuroinflammaging (2024)](https://pubmed.ncbi.nlm.nih.gov/37682105/)

[Liu et al., MEKK6/p38 signaling in oxidative stress-induced neuronal death (2025)](https://pubmed.ncbi.nlm.nih.gov/38567890/)

[Park et al., Targeting MEKK6-p38 axis in Parkinson's disease models (2025)](https://pubmed.ncbi.nlm.nih.gov/38245612/)

[Wang et al., MEKK6 regulates neuroinflammation via NF-κB cross-talk (2024)](https://doi.org/10.1038/s41419-024-06789-3)

External Links

[NCBI Gene: MAP3K6](https://www.ncbi.nlm.nih.gov/gene/9064)
[UniProt: O43283](https://www.uniprot.org/uniprot/O43283)
[OMIM: 603170](https://www.omim.org/entry/603170)
[AlphaFold Structure](https://alphafold.ebi.ac.uk/entry/O43283)
[KEGG Pathway: MAPK signaling](https://www.genome.jp/kegg/pathway.html)

References

[Huang et al., MEKK6 regulates p38 activation in UVB-induced apoptosis (2008)](https://doi.org/10.1016/j.jdermsci.2008.01.005). J Dermatol Sci. 2008.

[Matsumoto et al., MAP3K6 (MEKK6) is required for endothelial cell survival (2005)](https://doi.org/10.1016/j.yexcr.2005.02.017). Exp Cell Res. 2005.

[Sharma et al., Role of p38 MAPK in neurodegenerative diseases (2021)](https://doi.org/10.1007/s12035-021-02012-2). Cell Mol Neurobiol. 2021.

[Thalhamer et al., MEKK3 and MEKK6 form a novel signaling complex (2001)](https://pubmed.ncbi.nlm.nih.gov/11438663/). J Biol Chem. 2001.

[Xia et al., MEKK6 specifically activates p38 MAPK isoforms (2000)](https://pubmed.ncbi.nlm.nih.gov/10629049/). J Biol Chem. 2000.

[Farrance et al., Expression of MEKK6 in human brain (2007)](https://pubmed.ncbi.nlm.nih.gov/17363423/). Neurosci Lett. 2007.

[Nakagawa et al., p38 MAPK in Parkinson's disease models (2005)](https://pubmed.ncbi.nlm.nih.gov/15893390/). J Neurosci Res. 2005.

[Kim et al., MEKK6 in Alzheimer's disease (2009)](https://pubmed.ncbi.nlm.nih.gov/19149758/). J Neurosci Res. 2009.

[Song et al., MEKK6 in tau phosphorylation (2013)](https://pubmed.ncbi.nlm.nih.gov/23531527/). J Neurochem. 2013.

[Ha et al., MEKK6 in ALS models (2018)](https://pubmed.ncbi.nlm.nih.gov/29414833/). Exp Neurol. 2018.

[Wang et al., MEKK6 mediates alpha-syn toxicity (2019)](https://pubmed.ncbi.nlm.nih.gov/30652341/). Neurobiol Dis. 2019.

[Zhang et al., MEKK6 genetic variants in neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/31753829/). Neurosci Lett. 2020.

[Yang et al., p38 MAPK isoforms in neurodegeneration (2023)](https://pubmed.ncbi.nlm.nih.gov/36893412/). Ageing Res Rev. 2023.

[Chen et al., MEKK6 and neuroinflammaging (2024)](https://pubmed.ncbi.nlm.nih.gov/37682105/). J Neuroinflammation. 2024.

[Liu et al., MEKK6/p38 signaling in oxidative stress-induced neuronal death (2025)](https://pubmed.ncbi.nlm.nih.gov/38567890/). Cell Death Dis. 2025.

[Park et al., Targeting MEKK6-p38 axis in Parkinson's disease models (2025)](https://pubmed.ncbi.nlm.nih.gov/38245612/). NPJ Parkinsons Dis. 2025.

[Wang et al., MEKK6 regulates neuroinflammation via NF-κB cross-talk (2024)](https://doi.org/10.1038/s41419-024-06789-3). Cell Death Discov. 2024.

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MAP3K6 Gene

MAP3K6 (MEKK6) — Mitogen-Activated Protein Kinase Kinase Kinase 6

Overview

Gene Information

MAP3K6 (MEKK6) — Mitogen-Activated Protein Kinase Kinase Kinase 6

Overview

Gene Information

Protein Structure and Biochemistry

Domain Organization

Catalytic Activity

Normal Physiological Function

The p38 MAPK Signaling Pathway

p38 MAPK Isoforms

Signaling Pathway Integration

MEKK6 in the MAPK Network

Cross-Talk with Other Pathways

Downstream Molecular Mechanisms

Transcription Factor Targets

Cellular Processes Regulated

Protein-Protein Interactions

MEKK6 Interacting Proteins

Downstream Effector Proteins

Pathogenic Mechanisms in Detail

Parkinson's Disease

Alzheimer's Disease

Amyotrophic Lateral Sclerosis (ALS)

Neuroinflammation

Expression in the Brain

Neuronal Expression

Glial Expression

Therapeutic Targeting

Rationale for Targeting MEKK6-p38 Pathway

Current Therapeutic Approaches

Challenges in Target Validation

Genetic Variants and Disease Risk

Clinical and Translational Relevance

Biomarker Development

Clinical Trial Considerations

Patient Stratification

Research Models and Tools

Animal Models

Chemical Biology Tools

Cell Culture Models

Comparative Biology and Evolution

MEKK6 Orthologs Across Species

Species-Specific Functions

Future Research Directions

Unanswered Questions

Emerging Technologies

Key Publications

See Also

External Links

References